A display panel including a thin film transistor (hereinafter also referred to as a TFT) over a glass substrate, that is an active matrix drive display panel, has been fabricated by patterning various thin films by means of a light exposure method using a photomask.
As to such a display panel, technologies for effective mass production by which a plurality of display panels can be obtained from one mother glass substrate have been employed. The size of a mother glass has become larger from 300 mm×400 mm of the first generation in the early 1990s to 680 mm×880 mm or 730 mm×920 mm of the fourth generation in 2000. Accordingly, production technology has been improved, so that multiple display panels can be obtained from one mother glass substrate.
In the case where the mother glass substrate is small, patterning has been able to be performed relatively easily with the use of a light exposure apparatus. However, mother glass substrates have become larger; therefore, the entire surfaces of the mother glass substrate cannot be treated by a single exposure. Consequently, such a method as the area where a photoresist is applied is divided into plural blocks; light exposure is performed to each block; thus, the entire surface of a substrate can be exposed by repeating the light exposure process, or other methods have been developed. (Reference: Japanese Patent Laid-Open No. 11-326951).